This application is based upon and claims the benefit of priority of Japanese Patent Applications No. 2001-252753 filed on Aug. 23, 2001 and No. 2002-165486 filed on Jun. 6, 2002, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electromagnetic valve device for controlling fluid communication among a plurality of ports provided in a valve housing in such a manner that driving force of an electromagnetic drive member urges a valve body slidably disposed in the valve housing so as to be displaced against biasing force of a spring.
2. Description of the Prior Art
An electromagnetic valve device is known, in which a spool as a valve body slidably and reciprocatingly disposed in a cylindrical valve housing is displaced against biasing force of a spring by driving force of an electromagnetic drive member to control communication among a plurality of ports formed at a circumferential wall of the valve housing. The spring is retained by an end of an adjusting screw (acting as a stopper) screwed into an inner circumferential wall of the valve housing so that the biasing force of the spring is adjusted by turning the adjusting screw. For this purpose, the adjusting screw is turned until the adjusting screw reaches a predetermined position, or the adjusting screw is turned until pressure of oil flowing through the openings of the valve housing reaches a predetermined value when a given current is supplied to the electromagnetic drive member. After the adjusting screw has been turned and the biasing force of the spring has been set, the adjusting screw is fixed by staking, crimping or the like to the circumferential wall of the valve housing not to loose the screw engagement therewith.
However, the conventional valve housing and adjusting screw need higher manufacturing cost since both of the valve housing and adjusting screw are provided with threads to be engaged with each other. Further, when the adjusting screw is fixed to the valve housing by staking and the like, a position of the adjusting screw relative to the valve housing is likely displaced. To confirm no displacement of the adjusting screw, the pressure of oil of the electromagnetic valve device is again checked even after the adjusting screw has been fixed to the valve housing and, if the pressure of oil is out of the predetermined value, the electromagnetic valve is ejected as a failure, which results in higher manufacturing cost.
On the other hand, the electromagnetic valve device disclosed in JP-A-2000-124231 has a stopper for adjusting the biasing force of the spring acting on the spool, instead of the adjusting screw. The conventional stopper is formed in shape of a thin thickness wall cylinder having a bottom. The stopper is pushed into the inner circumferential wall of the valve housing by a certain length for adjusting the biasing force of the spring and, then, is fixed to the valve housing by stating or rolling in such a manner that a part of the thin thickness wall thereof is elastically deformed radially outward. Though the stopper and the valve housing are not provided with the threads, the valve housing has to be provided at inner circumference surface of the valve housing with a recess for stating or rolling. Accordingly, manufacturing cost of the electromagnetic valve device is still higher. Further, when the stopper is fixed to the housing after finishing the adjustment of the biasing force of the spring, the position of the stopper relative to the valve housing is likely to be still displaced.
To solve the problems mentioned above, it is an object of the present invention to provide an electromagnetic valve device in which a stopper for adjusting biasing force of a spring is press fitted to a valve housing at less manufacturing cost.
Another object of the present invention is to provide the electromagnetic valve device in which the stopper is fixed to the valve housing with an accurate axial position relative to the valve housing.
A further object of the present invention is to provide a method of manufacturing the electromagnetic valve device in which the stopper is accurately positioned relative to the valve housing with less number of pressing operations of the stopper into the valve housing.
To achieve the above objects, the electromagnetic valve device is composed of a valve housing having a cylindrical wall and a plurality of ports passing radially through the cylindrical wall, a valve member slidably accommodated in the cylindrical wall to control communications among the ports according to an axial displacement thereof, a spring which is positioned at the axial end of the valve housing and whose end is retained by an end of the valve member and urges the valve member toward another axial end of the valve housing, a stopper retaining another end of the spring and an electromagnetic drive member in contact with another end of the valve member for generating, when energized, a driving force to displace the valve member against a biasing force of the spring.
With the electromagnetic valve device mentioned above, the cylindrical wall is provided at an axial end with a small diameter portion whose wall thickness is thinner and the stopper is press fitted substantially to an inner circumferential surface of the small diameter portion of the cylindrical wall so that radially outward resilient deformation of the small diameter portion is larger than radially inward resilient deformation of the stopper. Even if the small diameter portion of the valve housing is expanded radially outward, the cylindrical wall where the plurality of ports are provided is not substantially deformed by the press fitting so that performance of the electromagnetic valve device is not adversely affected.
To rigidly press fit the stopper to the valve housing and to secure accurate axial position of the stopper relative to the valve housing, it is preferable that an axial length of the stopper is not shorter than 1 mm.
Further, preferably, the cylindrical wall is provided at an inner circumferential surface on a side of the axial end thereof with a small diameter inner surface, a large diameter inner surface and an inner step surface bridging the small and large diameter inner surfaces, and the stopper is provided with a large diameter outer surface press fitted to a part of the large diameter inner surface, a small diameter outer surface press fitted to a part of the small diameter inner surface and an outer step surface bridging the large and small diameter outer surfaces. A ring shaped space formed by the other part of the small diameter outer surface, the other part of the large diameter inner surface and the inner and outer step surfaces serves to accommodate chips and burrs due to press fitting. Accordingly, the chips and burrs are prevented from being mixed substantially into the oil so that the valve member can move smoothly in the valve housing for controlling oil communication among the ports.
Furthermore, in the electromagnetic valve device mentioned above, pressure of oil of the output port is variable according to the position of the valve member in the valve housing. The position of the valve member is governed by the biasing force of the spring and a driving force of the electromagnetic drive member that urges the valve member to displace against the biasing force of the spring. After the electromagnetic drive force, the valve member and the spring are assembled to the valve housing, the position of the valve member in the valve housing tends to be variable due to dimensional fluctuation based on manufacturing and assembling errors thereof so that the biasing force of the spring is variable. Accordingly, it is required that, in each of the electromagnetic valve devices, an axial position of the stopper relative to the valve housing is adequately adjusted each by each when the stopper is press fitted to the valve housing. To achieve this object, the following method is preferable,
(1) assembling the electromagnetic drive member, the valve member and the spring to the valve housing,
(2) pressing the stopper into the valve housing until an axial position of the stopper relative to the valve housing reaches a first position,
(3) measuring and memorizing pressure of oil of the output port at the first position as a first pressure by applying a given current to the electromagnetic drive member,
(4) further pressing the stopper into the valve housing beyond the first position until the axial position of the stopper relative to the valve housing reaches a second position,
(5) measuring and memorizing pressure of oil of the output port at the second position as a second pressure by applying the given current to the electromagnetic member,
(6) calculating a target position of the stopper relative to the valve housing corresponding to target pressure of oil of the output port when the given current is applied to the electromagnetic drive member based on a change ratio of a difference between the first and second pressures to a difference between the first and second positions, and
(7) further pressing the stopper into the valve housing beyond the second position until the axial position of the stopper relative to the valve housing reaches the target position.
According to the method of manufacturing the electromagnetic valve device mentioned above, the position of the valve member is adequately adjusted by pressing the stopper to the target position so that the target pressure of oil of the output port is accurately responsive to the given current applied to the electromagnetic drive member.